1. Field of the Invention
The present invention relates to a method for manufacturing small tubular lamps used for discharge lamps such as small metal halide lamps.
2. Description of the Prior Art
In manufacturing a small tubular lamp, for example, as shown in FIGS. 4 and 5, a tube stock a formed of glass, quartz, etc. is set on a glass lathe or a working device provided with a function similar to that of the glass lathe. At least one of left and right collets (bearings) is moved by a predetermined amount toward the center, while heating the tube stock a by a burner b in a rotating state, whereby padding is gathered on a predetermined portion of the tube stock a.
Then, the tube stock a is fully heated and made molten, and thereafter the predetermined portion of the tube stock a is covered with a mold c for blow molding. A predetermined pressure is applied into the tube stock a to inflate and suitably shape the tube stock a.
In metal vapor discharge lamps such as metal halide lamps, vapor pressure of a luminous material sealed into a luminous tube greatly influences the output, light color, etc. Therefore, it is desirable to minimize unevenness between individuals luminous tubes. Because of this, it is demanded in the process of manufacturing a luminous tube that dimensions of various parts, volumes, etc. need to have reproducibility with high precision.
Particularly, in a metal halide lamp whose power consumption is low (specifically, 100 W or less), severe improvement in precision is demanded with the trend of smaller types. The aforementioned conventional manufacturing method is not absolutely fulfilled with the aforesaid demand. Despite the fact that for example, a demand for a headlamp for an automobile or the like of which power consumption is low is anticipated, yield is poor and cost is high, thus posing a problem in that they cannot be sufficiently supplied to the market.
It is an object of the present invention to provide a method for manufacturing small tubular lamps capable of molding small tubular lamps with high working precision and with low cost.